The present invention relates to a squeegee device for a cylindrical stencil of a rotary screen printing machine, the device consisting of a flexible squeegee strip one edge of which is secured in a fitting whereas the other, free edge in operation, cooperates with the inner wall of the stencil. Such a device is known and is disclosed in co-pending patent application Ser. No. 383,155 filed on July 28, 1973 issued on Jan. 20, 1976 as U.S. Pat. No. 3,933,093, CIP of patent application Ser. No. 811,787 filed on Apr. 1, 1969, now abandoned.
A normal metal squeegee blade has a trailing edge which is in contact with the innerwall of the screen cylinder. This edge will yield to local pressure or uneven parts so that the trailing edge will not remain straight. There may also be other reasons for the trailing edge not to remain one straight line. These local flexures of the trailing edge are reflected in the printing result which renders the product of minor quality. By rigidifying the trailing edge of the squeegee blade, this disadvantage is avoided.
The rigidifying element may either be on the upper side of the squeegee blade or against the lower face. In the last mentioned embodiment, there is the possibility of making this element cylindrical, such that the nip-angle will remain constant not withstanding an increase or decrease in pressure exercised by the squeegee blade.
In operation, a quantity of paste or paint supplied within the stencil is pressed through the stencil perforations onto the material which contacts the outside of the stencil, e.g., a web of fabric or a paper strip. The squeegee device has a double function since adjusting the squeegee strip will determine both the quantity (or output) of the paste reaching the material through the stencil and the penetration depth of the printing paste into the material (in printing textiles).
The above-mentioned quantity or output depends on the angle between the squeegee strip and the inner wall of the stencil. The penetration depth depends on the force with which the squeegee strip is pressed against the inner surface of the stencil. In the conventional squeegee devices these two functions cannot be separated but are dependent upon each other. If, for example, it is desired to change the squeegee angle in order to influence the quantity of paste which is pressed through the stencil, this change of angle will mostly only be achieved by means of the compressive force. Inversely, when the penetration depth must be varied, one has to adjust the compressive force of the squeegee strip, which automatically results in a change of the squeegee angle and consequently a change of the output or applied coating.